Plaster of paris cast and material for use in making same



Patented Mar. 26 1940 PLASTEB OF PARIS CAST AND MATERIAL FOR USE IN MAKING SAME Raymond E. Reed, Chicago, Ill., assignor to The Kendall Company, Walpole, Mass., a corporation of Massachusetts No Drawing.

11 Claims.

This invention relates to plaster of Paris bandages and particularly to the foundation fabrics utilized in such bandages.

Plaster of Paris bandages may be made by either the wet or the dry process. In the wet process, the powdered plaster is compounded with a solution of a suitable adhesive material until it is reduced to the consistency of a thick cream or paste, after which it is spread upon the foundation fabric, which is then dried and cut into the desired lengths and finally rolled into bandage form. In the dry process, which is the one more commonly'used, the fabric is first cut into strips of the desired width and the plaster, in the dry condition, is spread on the strips in the desired quantity. The strips with the dried powder incorporated therein are then rolled into bandage form. Whether made by the wet or by the dry process the rolled bandages are pre- 20 pared for casting by immersing them in water until the plaster has been thoroughly moistened,

whereupon they are applied to the arm, leg or other member upon which the cast is to be formed.

The dry process, because of its simplicity and cheapnes's, is preferred by the 'great majority of plaster bandage users. and a plaster of Paris having the desired setting properties and combine the two in the preparation of their product. The fabrics used are gen- 'erally of the stiffened variety, because unsized fabrics cannot be torn readily into strips ofthe desired width. The latter are soft and difficult to handle during the application of the plaster 35 and the edges of the strips ravel badly. On the other hand, crinoline tears very readily, takes the plaster very well, and does not ravel because the yarns are bound together by the stiffening material. I It is well known that plaster of Paris is a very sensitive material. The addition of small quantitles of foreign substances to plaster-water mixtures may profoundly afiect the properties of the resulting cast. For example, the addition of an 45 inorganic salt such as potassium sulphate will very markedly accelerate thesetting time of such a mixture. On the other hand, minute additions of protein colloids, such as gelatine or blood will significantly retard the setting time and'impair 50 the strength of the cast. Because of the sensitive nature .of plaster, the stiffening or sizing agents incorporated in the crinoline used in the preparation of bandages have justifiably long been under suspicion by the users of plaster of Paris bandages.

Thus they buy crinoline Application March 29, 1937, Serial No. 133,661

In actual practice, pure corn and potato starches and thin boiling varieties of these products have been the preferred materials used as stifiening agents in the preparation of. foundation fabrics for these bandages. Such materials 5' are cheap and have remarkable stiffening power when incorporated in woven fabrics. In their effect on plaster of Paris, however, theyare far from ideal materials. This is true because these substances are colloidal in nature and exert, to 10 some extent, the undesirable effects previously described in connection with gelatin and, blood.

A problem which is also of considerable importance in plaster of Paris bandages and one related to the foundation fabric used, is the manner in which they wet out when immersed in water. Frequently the surgeon in using these band ages, encounters dry areas of plaster in the bandage which have not been penetrated by water during the normal immersion period. This difficulty is generally associated with tightly wound bandages and is often caused by the poor wetting-out properties of the sizings used.

An additional very important property of casts. prepared with plaster bandages is the rate at which they dry or set, A cast, at the setting point, has usually achieved only one-third of its potential strength. The additional strength depends upon thevolatilization of the excess water which is absorbed during the immersion step.

In this operation, the bandage normally picks up two to three times the quantity of water necessary to convert the available plaster into, gypsum. Because the normal colloidal sizing materials have pronounced gel-forming tendencies, they imbibe water at a rapid rate during and immediately following the immersion operation. This water is held in the cast and volatilized at a slow rate, thereby maintaining the cast in a moist condition for a substantially longer period of time'than otherwise would be the case. In fact, under some humidity conditions, a decrease in cast strength may well occur. This phenomenon 'is traceable to the fact that when the plaster remains wet, it slowly becomes softer and loses strength. While the. causes of this loss of strength are not well known, they appear to mvolve some change in the internal crystalline structure of the set plaster.

The present invention is especially. concerned with the problems presented byv the considerations above described, and it aims to improve plaster of Paris bandages, and the foundation fabrics used in making them, with a view to des5 visinga thoroughly practical solution for these problems.

I have discovered that the objectionable chararteristics of the sized fabrics-used for these purposes can be greatly reduced by replacing a high proportion of the starch, or other colloidal adhesive employed as a stifiening agent, with some inert non-colloidal reinforcing agent or stiffener,- such as china clay. For example, as much as 50% of the starch sizing may be replaced by china clay while still producing a product prac tically as stiff as that made with the starch alone and greatly reducing the disadvantages of the starch sized fabric.

A far better product, however, is obtained by replacing the starch sizing with a mixture of a substantially non-colloidal adhesive and a non colloidal stiffening agent of the general nature of china clay. I have found'that dextrines are particularly suitable for this purpose and have the advantage of being economical to use. They are the products of the acid and/or heat degradation of pure starches and are easily dissolved in water. While, therefore, they are adhesives of a starchy nature, they have negligible colloidal properties and therefore avoid the objections-inherent in the-use of the common starch sizings. Ifused alone, dextrine would not give to the fabric the desired tearing properties, nor would it impart to the fabric that stiffnem which is required in making plaster casts. a They can, however, be readily mixed with n'on-colloidal stiffening and filling agents of a mineral nature, such as china clay, talc, feldspar, calcium sulphate, diatomaceous earth, and others, which will cooperate with the adhesive to give the fabric the necessary degree of stiffness. The fabric fonndations made by either of these methods can, of course, be loaded with plaster of Paris by either the wet or dry processes commonly used in connection with the manufacture of prior art bandages of this type. It will be observed that the stiffening agents above mentioned are all inert with respect to both water and the plaster of Paris with which the foundation fabric later is loaded prior to being used as a bandage or cast.

In practicing my invention, a typical mode of procedure is as follows:

A sizing bath is first prepared by dissolving five pounds of dextrine in one gallon of water and then with this solution 1.7 pounds of china clay, the mixture then being brought to a boil. A crinoline is then prepared by passing a 32/28 mesh gauze through the sizing bath, running between squeeze rolls, and then drying by any suitable method. The resulting fabric will be found to contain approximately- %01 the dextrine-china clay composition. The material so produced will also be found to tear very easily and uniformly, the fabric will take the'plaster readily and no undue amount other relatively non-colloidal-adhesives can be used to replace them such, for example, as maltose, glucose, and others. It is recognized that there is no exact line of demarcation between colloidal and non-colloidal material. but there is an easily recognizable difference between such relatively non-colloidal substances as those above mentioned and the various forms of starch which have been used heretofore in sizing these foundation fabrics and which have very pronounced colloidal properties.

-.The color of the crinoline prepared in accordance with the foregoing method may also be materially improved by the additionof zinc oxide, titanium oxide, and other pigmenting agents.

While I have herein described typical embodiments of my invention, it will be understood that the invention may be embodied in other forms without departing from the spirit or scope thereof. For example, other suitable fabrics may be substituted for the particular gauze mentioned above.

Having thus described my invention, what I desire to claim as new is:

1. A plaster of Paris bandage comprising an open mesh fabric sized with a mixture of a water softenable stiffening material and a substantially non-colloidal, water insoluble filler material, said mixture being substantially inert chemically with reference to water, and said fabric being coated with plaster of Paris.

2. A plaster of Paris bandage comprising .an open mesh fabric sized with a mixture of a water softenable stiffening material and an inert reinforcing agent, said mixture being substantially inert chemically withreference to water, and said fabric being coated with plaster of Paris.

3. A plaster of Paris bandage comprising an open mesh fabric sized with a mixture of an adhesive anda substantially non-colloidal mineral stiffener, said mixture being substantially inert chemically with reference to water, and said fabric being coated with plaster of Paris.

4. A plaster of Paris bandage comprising an open mesh fabric sized with a mixture of a substantially non-colloidal, water softenable adhesive, and a substantially non-colloidal water insoluble stiffener, said mixture being substantially inert chemically with reference to water, and said fabric being coated with plaster of Paris.

5. A plaster of-Paris bandage comprising an open mesh fabric sized with a mixture of a substantially non-colloidal, water softenable adhesive, and a water insoluble, reinforcing agent, said mixture being substantially inert chemically with reference to water, and said fabric being coated with plaster of Paris.

6. A plaster of Paris bandage comprising an open mesh fabric sized with a mixture of dextrine and a substantially non-colloidal mineral stiffening agent, said mixture being substantially inert chemically under normal temperature conditions with reference both to water and to plaster of Paris, and said fabric being coated with plaster of Paris.

'7. A plaster of Paris bandage comprising an open mesh fabric sized with a mixture of dextrine and china clay, said mixture being substantially inert chemically under normal temperature conditions with reference both to water and to plaster of Paris, and said fabric being coated .with plaster tially inert chemically with reference to water,

said material including an inert reinforcing agent, and said fabric being loaded with plaster of Paris.

9. A plaster of Paris bandage material comprising a foundation fabric sized with a substantially non-colloidal mixture of an adhesive and a finely divided water insoluble stiffener, and a coating of plaster of Paris on said sized fabric, said mixture being substantially inert chemically under normal temperature conditions with reference to both water and plaster of Paris.

10. In a plaster of Paris bandage, an open mesh foundation fabric sized with a mixture of a water softenable stiffening material and a substantially non-colloidal, Water insoluble filler material, said mixture being substantially inert chemically with reference to water.

11. In a plaster of Paris bandage which comprises an open mesh fabric, a sizing for said fabric, and a coating of plaster of Paris, a sizing material comprising a mixture of an adhesive and a substantially non-colloidal mineral stiffener, said mixture being substantially inert chemically. 

